Lionel O. Bouthillette

High Quality Hydrothermal ZnO Crystals

Zinc Oxide crystals have historically been grown in hydrothermal autoclaves with a basic mineralizer; however, doubts have been raised about the quality of such crystals because they have often exhibited large x-ray rocking curve widths and low photoluminescence (PL) yield with large linewidths. Several ZnO crystals were grown hydrothermally and sliced parallel to the c-plane. This resulted in opposite surfaces (the C + and C - ) exhibiting pronounced chemical and mechanical differences. Different surface treatments were investigated and compared by PL both at room temperature and liquid helium temperatures, and by double axis X-ray rocking curve measurements. The high quality of hydrothermally-grown ZnO is substantiated by the narrow rocking curve widths and sharp PL peaks obtained. A critical factor in obtaining these results was found to be surface preparation.

Characterization of Eu- and Y-polytantalate Films Deposited by RF Diode Sputtering

Using radio frequency (RF) diode sputtering of sintered stoichiometric (Eu,Y) 2 O 3 :7Ta 2 O5 ceramic targets, thin films (0.2–0.6 m) of Eu- and Y-polytantalates, and their solid solution Eu x Y 1-x Ta7O19 were deposited on fused silica, Si (100) and sapphire (001) substrates under various sputtering conditions. As-grown films were amorphous, and were crystallized by post-annealing in oxygen at 900 to 1000 °C. The influences of deposition gases (Ar and O 2 -partial pressure) substrate material, deposition time, substrate temperature, and post-annealing time and temperature on the structural, morphological and photo-luminescence (PL) properties of Eu 3+ -ions in the films have been studied and compared to properties of sintered (Eu,Y)Ta 7 O 19 ceramic and EuTa 7 O 19 single crystals.

Epitaxial Growth and Structural Characterization of Single Crystalline ZnGeN 2

A new nitride semiconductor, single crystalline ZnGeN 2 has been successfully grown by MOCVD for the first time. The epitaxial ZnGeN 2 is found to be of hexagonal wurtzite lattice without ordering of the zinc and germanium atoms in the pseudomorphic Group III sublattice. Lattice constants of the ZnGeN 2 are a = 3.186 ± 0.007 A, c = 5.174 ± 0.012 A, which gives c/a = 1.624.

Optical and Dielectric Properties of Eu- and Y-Polytantalate Thin Films

Due to their highly efficient photo-luminescent (PL) characteristics, the physical properties of rare-earth polytantalates, RETa7O19 (RE=Eu and Y) were further studied. AFM, SEM, HRTEM, x-ray reflectometry, spectroscopic ellipsometry and standard dielectric testing were used to determine film thickness, roughness, index of refraction, band-gap, dielectric constant, leakage current and breakdown field for as-deposited (amorphous) and post-annealed (crystalline) films. Structural and morphological properties of the Film/SiO2/Si interfaces were also examined.

High electron mobility in free-standing GaN substrates

High peak electron mobilities were observed in free-standing c -plane GaN substrates. Two layers, a low mobility degenerate layer and a high mobility bulk layer, were present in these samples. The carrier concentrations and mobilities for the layers were extracted using two methods: 1) magnetic field dependent Hall effect analysis and 2) a simple two carrier model with the assumption that one of the layers is degenerate. In addition, measurements were performed after etching away the degenerate layer. The mobility of the bulk layer is found to peak at nearly 8000 cm 2 /Vs at 60K using the magnetic field dependent Hall effect data. Record room temperature mobility for bulk GaN of 1190 cm 2 /V s was measured.